Some electronic devices are provided to be worn on a body. Such electronic devices are generally referred to as wearable devices, and various types of wearable devices have been developed. For example, wearable devices have been provided in a head-mounted type (e.g., glasses), a wrist wearable type (e.g., watches or wristbands), a contact lens type, a ring type, a shoe type, or a clothing type so that the wearable devices may be attached to, or detached from, a body or clothing. The wearable devices allow electronic devices to be worn on the body, such as clothes or glasses, to improve the portability and accessibility of the electronic devices.
Among the wearable devices, head-mounted wearable devices, such as an HMD (head-mounted display), have been widely developed. The HMD may provide a see-through type of screen for providing augmented reality (AR), or a see-closed type of screen for providing virtual reality (VR).
The see-through type HMD may provide a screen that has additional information, which can hardly be obtained in the real world, by synthesizing and combining a real world-based screen with virtual objects using the properties of a semi-transparent lens. The HMD in the see-closed type may provide two displays so that content (games, movies, streaming, or broadcast data) received from the outside may be displayed on the separate displays in order to allow the user to concentrate on the content.